The present invention relates to a tripping device for a safety device for protecting vehicle occupants in the event of a side crash of a vehicle, and has a deformation sensor arranged either in or directly behind an outer skin in a lateral region of the vehicle and that determines a deformation rate, a central transverse acceleration sensor mounted on a longitudinal axis of the vehicle, and an evaluation circuit. The evaluation circuit is coupled to the deformation sensor and the transverse acceleration sensor and is responsive to electrical signals from the deformation sensor and the transverse acceleration sensor to trip the safety device in the event of a dangerous crash of the vehicle.
Passive safety devices which in the event of an accident are tripped without the help of the vehicle occupants have long been known, including the air bag system, which has meanwhile been installed in mass production in motor vehicles and in which an air cushion is inflated automatically in the event of a crashing of the vehicle against an obstacle. These mass produced air bags are generally frontal crash systems which are intended to protect the driver and front passenger from a hard impact against the steering wheel, the windshield or the dashboard.
Furthermore, it is also known for air bag systems to be arranged on the vehicle side panels or doors in order to improve the protection of the vehicle occupants in the event of a side collision of the vehicle. In the ideal case, the lateral air bag has a relatively large volume in the inflated and deployed state and extends over the entire height of the side panel or door and covers a window opening.
Since in the lateral region motor vehicles have only minimal deformation zones which are able to absorb a portion of the collision energy, the period available for bringing the lateral air bag into a protectively effective state is very much shorter than in the event of a frontal crash. Consequently, high demands for a quick and reliable response are placed on a sensor and an evaluation circuit for detecting a side crash.
U.S. Pat. No. 3,851,305 discloses a tripping circuit for detecting a frontal crash and an oblique crash, which evaluates the signals of a crash sensor arranged in the front region of the vehicle and of a central acceleration sensor. The tripping circuit transmits a signal for tripping to the safety device as soon as the acceleration signal overshoots a threshold value. The threshold value is influenced, in turn, by the crash sensor in such a way that when a crash is recorded the threshold value is reduced. The reduction follows a prescribed temporal characteristic, in which the threshold value reassumes the initial value after a predetermined time. Although this tripping circuit could also be used in conjunction with a crash sensor mounted in the lateral region of the vehicle, an adaptation to the very time-critical conditions of detecting a side crash by a low tripping threshold would clearly increase the risk of undesired tripping due to a transverse acceleration that was strong, but lasted only briefly and was not dangerous.
Furthermore, German Pat. No. Document DE-A-3,716,168 describes a deformation sensor which is arranged below the outer skin in the lateral region of the vehicle and extends over the entire width of a door. The deformation sensor is constructed from two signal elements which are arranged at a short separation one behind another and respond one after another as soon as the outer skin is deformed by an external effect. Proposals for the signal elements are, on the one hand, light pipes which trip a signal in the event of a crash-induced functional disturbance ,and, on the other hand, pressure transmitters in the bearings of structural elements in the lateral region of the vehicle. The time interval from the first signal to the signal of the second signal element depends on the given spatial separation of the two signal elements and on the rate at which an obstacle dents the motor vehicle. Using this measure of the deformation rate, it is possible (to a limited extent) to conclude there is an imminent danger to the occupants, with the result that given overshooting of a critical deformation rate the safety device is tripped. In this way, unnecessary tripping of the safety device is avoided when an obstacle deforms the outer skin of the vehicle very slowly, as is the case when the vehicle strikes an obstacle at low speed, the deformation certainly possibly being substantial.
In the use of the deformation sensor described above, disadvantages arise from the circumstance that the sensing is limited exclusively to the local deformation rate at the site of the quickest deformation. Specifically, the local deformation rate is not a variable which can be used to conclude unambiguously on the kinetic energy of the striking object. For example, an object with a small impact surface such as a hammer, can indent at a high local deformation rate and lead to tripping of the safety device, although its kinetic energy is very far from sufficient, after expiry of the first deformation phase, to impart to the vehicle a transverse acceleration which could be dangerous to the occupants.
It is an object of the invention to construct a tripping device of the above-described type, which responds quickly and reliably in the event of a side crash which is dangerous for the occupants, but on the other hand rules out an undesired tripping caused for example by a hammer strike or a collision which is not dangerous.
This and other objects are achieved by the present invention which provides a tripping device for a safety device for protecting vehicle occupants in the event of a side crash of a vehicle, and has a deformation sensor arranged either in or directly behind an outer skin in a lateral region of the vehicle and that determines a deformation rate, a central transverse acceleration sensor mounted on a longitudinal axis of the vehicle, and an evaluation circuit. The evaluation circuit is coupled to the deformation sensor and the transverse acceleration sensor and is responsive to electrical signals from the deformation sensor and the transverse acceleration sensor to trip the safety device in the event of a dangerous crash of the vehicle. The evaluation circuit includes a deformation evaluator that receives and processes the signals of the deformation sensor and transmits a trigger signal in the event of a critical deformation, an acceleration evaluator coupled to the deformation evaluator and the transverse acceleration sensor, the acceleration evaluator receiving and conditioning the signal from the transverse acceleration sensor by weighted integration, so that integration is started by the trigger signal of the deformation evaluator, and a comparator coupled to the acceleration evaluator and which compares the conditioned signal with a prescribed threshold value and transmits a tripping signal to the tripping device upon overshooting of the threshold value.
The aforementioned objects are also achieved by another embodiment of the present invention which provides a tripping device for a safety device for protecting vehicle occupants in the event of a side crash of a vehicle, and has a deformation sensor arranged either in or directly behind an outer skin in a lateral region of the vehicle and that determines a deformation rate, a central transverse acceleration sensor mounted on a longitudinal axis of the vehicle, and an evaluation circuit. The evaluation circuit is coupled to the deformation sensor and the transverse acceleration sensor and is responsive to electrical signals from the deformation sensor and the transverse acceleration sensor to trip the safety device in the event of a dangerous crash of the vehicle. The evaluation circuit includes a deformation evaluator that receives and processes the signals of the deformation sensor and transmits a control signal corresponding to the deformation rate in the event of a critical deformation, an acceleration evaluator coupled to the transverse acceleration sensor and that conditions the acceleration signal, a comparator coupled to the acceleration evaluator and which compares the conditioned signal with a prescribed threshold value and transmits a tripping signal to the tripping device upon overshooting of the threshold value, and a threshold generator coupled to the deformation evaluator and that prescribes the threshold value to the deformation evaluator as a function of control signals provided to an input of the threshold generator, the prescribed threshold value being reduced in the event of a critical deformation, the reduction being the greater the higher the determined deformation rate.
The tripping device according to the invention ensures that a quickly indenting object trips the safety device only if its kinetic energy also suffices to impart to the vehicle a significant and lasting transverse acceleration. The integration of the acceleration signal prevents the safety device from being tripped by an acceleration pulse which is strong but only brief. On the other hand, the system reacts very quickly because the integration is started by a signal from the deformation sensor. Furthermore, it can be provided that the tripping sensitivity is increased in the event of a critical impact recorded by the deformation sensor, as a result of which the response time is also shortened.
Certain embodiments of the invention advantageously use a known deformation sensor which is suitable for determining the deformation rate and is described, for example, in German Patent No. Document DE-A-3,716,168 A1. According to the invention, the enhancement in the tripping sensitivity, occurring in a crash, depends on the deformation rate specifically more strongly the higher the determined deformation rate. As a result, a deformation which, although slow, is strong, is prevented from initiating an unnecessarily strong enhancement of the tripping sensitivity. On the other hand, a quick response is ensured in the event of a rapid deformation. The tripping sensitivity is thus matched to the time which is available for a tripping decision. In the event of a quick deformation, priority attaches to a quick response and, in the event of a slow deformation, to the avoidance of spurious tripping.
Other objects, advantages and novel features of the present invention will become apparent from the following detailed description of the invention when considered in conjunction with the accompanying drawings.